BUG/MEDIUM: dns: send messages on closed/reused fd if fd was detected broken

BUG/MEDIUM: dns: send messages on closed/reused fd if fd was detected broken

This fix complete this incomplete bug fix '(751872e4)':
'BUG/MEDIUM: dns: reset file descriptor if send returns an error

This previous patch detects error on fd and close this one but the code
continues the loop on pending queries and try to send them using the
previously closed fd which could be reused by an other thread.

This patch stop to send queries on this fd and count them on
snd_error counter.

This patch applies on branch 2.3 and all this stuff is already
fixed in newer version by '(d26a6237ad)':
'MEDIUM: resolvers: split resolving and dns message exchange layers'

This patch should be backported on all branches including the previous
fix '(751872e4)':
'BUG/MEDIUM: dns: reset file descriptor if send returns an error'